1. Field of the Invention
The present invention relates to batteries, thermoelectric and photoelectric, especially to photoelectric cells containing selenium or tellurium and containing copper, lead, or zinc. More specifically, the invention relates to a process for fabricating a photoelectrochemical solar cell consisting of n-CuInSe.sub.2 electrode material and having an iodide/iodine redox couple.
2. Description of the Prior Art
An economic solar cell should have a solar conversion efficiency of over 10%. A 5.6% solar efficiency was observed for a liquid junction photoelectrochemical cell using n-CuInSe.sub.2 as the photoanode, etched in 3:1 (V/V) HCl:HNO.sub.3, H.sub.2 O rinse, 0.1 M KCN and H.sub.2 O rinse, and with a polysulfide redox electrolyte. Y. Mirovsky and D. Cahen, Appl. Phys. Lett. 40(8), 727 (1982). This system showed stable output efficiency, although it was recognized that improvement was needed in open circuit voltage and fill factor if the cell was to be of practical use as a solar cell. One possible cause for the low open circuit voltage was speculated to be microcracks and pits on the surface of the electrodes.
An improved cell using n-CuInSe.sub.2 with different interface kinetics is reported to have produced better efficiency. S. Menezes, H. Lewerenz, and K. Bachmann, Nature 305, 615 (1983). The same photoanode of the ternary chalcopyrite material and the same etchant were used as in the previous cell. The electrolyte consisted of 2 M I.sup.-, 2.5 M HI, 50 mM I.sub.2 and 20 mM Cu.sup.+. An efficiency of 9.5% was reported with an output that was considered nearly stable, which was attributed to the formation of an interfacial film.
Other known etchants include Br.sub.2 /MeOH, which has been used on p-CuInSe.sub.2. H. Haupt and K. Hess, Inst. Phys. Conf. Ser. 35, 5 (1977).
Further improvements in efficiency as well as attainment of complete stability are clearly desired in order to improve the economics of solar cell utilization on a widespread basis. To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the photoelectrochemical cell of this invention may comprise the following.